The term event refers to any particular or specific occurrence within the project life cycle. This can refer to a ;particular activity that takes place within the project, it can refer to any particular meeting that may be conducted for the purposes of discussing anything related to the project, it can refer to a specific occurrence related to the actual provision of the final deliverable to the client. The entirety of the project is in reality just a series of one event after another, and it is up to the project team and the project team leader to devise a sophisticated and effective means of keeping these events in some sort of proper and convenient order in hopes of assuring that everyone stays on the same page, and that all of the events that make up a project go in the proper sequence and that all of these events are completed or undertaken successfully and efficiently if at all possible.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.